1. Field of the Invention
The present invention relates to a door opening/closing apparatus that automatically opens and closes a door of a vehicle by an electric actuator.
2. Description of the Related Art
As a door opening/closing apparatus for opening and closing a door that is supported by a vehicle body such that the door can open and close in a vertical direction, a door opening/closing apparatus that opens and closes a back door provided on a rear portion of the vehicle body by a drive mechanism is conventionally known (see, for example, Japanese Patent No. 3795325). According to the door opening/closing apparatus disclosed by Japanese Patent No. 3795325, a drive motor is provided in a rear portion of a vehicle body. As shown in FIG. 10, the door opening/closing apparatus includes a swing arm 62 whose one end is connected to a rotation shaft 61 of the drive motor, and a connection link 64 that connects the swing arm 62 and a hack door BD with each other. The door opening/closing apparatus drives the drive motor to rotate the swing arm 62 connected to the rotation shaft 61, thereby automatically opening and closing the back door BD through the connection link 64.
As shown in FIG. 10, in the door opening/closing apparatus of Japanese Patent No. 3795325, when the swing arm 62 starts rotating in a clockwise direction by a driving force of the drive motor, the driving force of the drive motor is transmitted from the swing arm 62 to the connection link 64. Therefore, the driving force of the drive motor is output as a force F0 from the connection link 64 to the back door BD through a connection shaft 65. At this time, when the closed back door BD is driven to its opening direction, a torque (=F2×L2) obtained by multiplying a distance L2 between the pivot shaft 67 and the connection shaft 65 by a component force F2 of the force F0 in a direction orthogonal to a line segment that connects the pivot shaft 67 and the connection shaft 65 with each other is applied to the pivot shaft 67 of the back door BD.
However, it is difficult to increase the component force F2, the distance L2 and the driving force of the drive motor due to the following reasons.
The component force F2 is explained first. As shown in FIG. 10, when the swing arm 62 starts rotating in the clockwise direction by the driving force of the drive motor, a connection shaft 63 of the connection link 64 rotates in the clockwise direction around the rotation shaft 61. According to this configuration, the connection link 64 moves such that the connection shaft 63 approaches the pivot shaft 67 to operate the back door BD in its opening direction. Accordingly, the force F0 output from the door opening/closing apparatus to the back door BD is applied in a direction toward the pivot shaft 67 in a state where a moving direction of the connection link 64 is different from a moving locus of the connection shaft 65 centered on the pivot shaft 67. As a result, the component force F2 that actually rotates the back door BD in its opening direction becomes smaller than the force F0.
If a torque applied to the back door BD when the drive motor is driven to open the back door BD is constant, it is necessary to increase the distance L2 when the component force F2 is small. In this case, the distance L2 can be increased by moving a position of the connection shaft 65 in a downward direction of the back door BD. If the position of the connection shaft 65 is moved in this manner; however, the door opening/closing apparatus is placed at a front portion of the vehicle and there is a possibility that a space in a vehicle interior is sacrificed. The movement of the connection link 64 can be applied as the force F0 directly rotating the back door BD by bringing the moving direction of the connection link 64 close to the moving locus of the connection shaft 65 centered on the pivot shaft 67. However, because the moving direction of the connection link 64 is directed to a longitudinal direction of the vehicle, there is a possibility that the space in the vehicle interior is sacrificed.
Furthermore, when it is difficult to increase the component force F2 and the distance L2 due to a layout of the vehicle, it is also possible to increase the component force F2 by increasing the driving force of the drive motor. However, because there is a general trend that the size of the drive motor is increased, there is a possibility that the space in the vehicle interior is sacrificed.
As described above, because the driving force of the drive motor is transmitted from the swing arm 62 to the back door BD through the connection link 64, the door opening/closing apparatus disclosed in Japanese Patent No. 3795325 has a problem that there is a possibility that the space in the vehicle interior is sacrificed, and the transmission efficiency of the driving force generated by the drive motor is poor.